Richard Biener <richard.guent...@gmail.com> writes:
> On Thu, Apr 10, 2025 at 10:10 PM Richard Sandiford
> <richard.sandif...@arm.com> wrote:
>>
>> PR119610 is about incorrect CFI output for a stack probe when that
>> probe is not the initial allocation. The main aarch64 stack probe
>> function, aarch64_allocate_and_probe_stack_space, implicitly assumed
>> that the incoming stack pointer pointed to the top of the frame,
>> and thus held the CFA.
>>
>> aarch64_save_callee_saves and aarch64_restore_callee_saves use a
>> parameter called bytes_below_sp to track how far the stack pointer
>> is above the base of the static frame. This patch does the same
>> thing for aarch64_allocate_and_probe_stack_space.
>>
>> Also, I noticed that the SVE path was attaching the first CFA note
>> to the wrong instruction: it was attaching the note to the calculation
>> of the stack size, rather than to the r11<-sp copy.
>>
>> Bootstrapped & regression-tested on aarch64-linux-gnu. I'll push on
>> Monday if there are no comments before then. I'd appreciate a second
>> pair of eyes though, since this is a sensitive area.
>
> Do you happen to know if the backports to older branches you provided for
> the change that triggered this issue (in particular to GCC 7) are also
> affected?
GCC 7 and GCC 8 should be ok. The bug relies on stack protection being
enabled (-fstack-protector-strong for the testcase in the PR, but just
-fstack-protector for others) and that was added in GCC 9.
> The testcase from the PR does not fail in the reported way for me, but I guess
> that very much depends on "details".
Oh, even on trunk? Does adding:
volatile int unused[N] = {};
to main for various N change things?
Thanks,
Richard
